1. Field of the Invention
The present invention relates to an apparatus of detecting infrasound, which can detect infrasound by a differential pressure method.
2. Discussion of Related Art
Infrasound is a sound wave in a low frequency band between 0.01 and 20 Hz, which is lower than an audible frequency for human beings. Infrasound observation is one of the technologies used in monitoring of nuclear tests occurring from all over the world as a part of an International Monitoring System (IMS) technique, which is a monitoring system of the Comprehensive Test Ban Treaty (CTBT) along with monitoring using seismic waves, hydroacoustic waves or radionuclides. Today, infrasound provides important data to research for discrimination between artificial explosion and earthquake occurring on the earth's surface and in the air, in addition to the monitoring of nuclear tests.
The research on infrasound was on the rise as an important method for monitoring nuclear tests in the atmosphere in 1940s to 1950s, but declined by the treaty of banning nuclear weapons in the atmosphere and under water of 1963. However, as the CTBT was proposed by the United Nations in 1996, and to this end, the IMS for the task of detecting nuclear tests in the world was operated, worldwide infrasound monitoring stations are being established according to an IMS construction plan, and today, research using acquired data is actively being conducted in all over the world.
Sound sources of infrasound may include a nuclear test, volcanic eruption, the movement of a meteorite, typhoon, landslide, aurora, earthquake, artificial explosion, a supersonic airplane, missile launching, atmospheric flow change in a mountainous area, a flight vehicle in the atmosphere, etc. An observation object is a change in atmospheric pressure occurring by such a sound source, and an apparatus for observing IMS infrasound should measure standard volume displacement caused by an atmospheric pressure as low as 0.01 microbar using a microbarometer, and have a consistent reaction in a low frequency band of 0.01 to 20 Hz.
Meanwhile, since infrasound to be detected propagates into the air with variable atmospheric pressures, an apparatus for detecting infrasound generally needs a component for filtering pressure variation of a frequency according to a significant frequency band of the sound source to be studied, and therefore research on such a component is now being conducted.